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Energy and Nutrient RelationsChapter 7

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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Energy Sources• Organisms can be classified by trophic

(feeding) levels. Autotrophs use inorganic sources of

carbon and energy. Photosynthetic: Use CO2 as carbon

source, and sunlight as energy. Chemosynthetic: Use inorganic

molecules as source of carbon and energy.

Heterotrophs use organic molecules as sources of carbon and energy.

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Photosynthesis• The synthesis of organic molecules using CO2 as a

source of carbon and light as the energy source Light travels in waves in particles called

photons Photosynthetically Active Radiation (PAR)

Wavelengths of light used in photosynthesis (approx. 400-700 nm)

Photosynthesis converts CO2 to Glucose!

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Photosynthesis

• Chlorophyll absorbs photons. Landscapes, water, and organisms can

all change the amount and quality of light reaching an area.

There are different ways that photosynthesizers do it!

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Photosynthetic Pathways• Three different pathways

C3 Photosynthesis C4 Photosynthesis CAM Photosynthesis

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Photosynthetic Pathways - C3 Photosynthesis Used by most plants and algae. CO2 + ribulose bisphosphate (5 carbon sugar) =

phosphoglyceric acid (3 carbon acid) To fix carbon, plants must open stomata to let

in CO2 . Water gradient may allow water to

escape.

Where would you expect to find C3 plants?

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Some C3 Plants

Wheat, rice, potatoes

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Photosynthetic Pathways - C4 Photosynthesis Reduces internal CO2 concentrations.

Increases rate of CO2 diffusion inward. Need fewer stomata open – conserves water!

Photosynthesis separated in space – C4 molecule formed in mesophyll, then photosynthesis occurs in bundle sheath cell

Where would you expect to find C4 plants?

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Some C4 plants

Corn, sugarcane

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Photosynthetic Pathways• CAM Photosynthesis

(Crassulacean Acid Metabolism)

Photosynthesis separated in time

Found mainly in succulent (water-storing) plants in arid environments Carbon fixation takes place

at night – greatly reduced water loss

Low rates of photosynthesis.

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Results from the 3 photosynthetic pathways

• C3 plants lose 380-900 g water for every gram of dry tissue produced

• C4 plants lose 250-350 g water per gram of tissue produced

• CAM plants lose 50 g water per gram of tissue produced

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Chemosynthetic Autotrophs• Synthesize organic molecules

using CO2 as a carbon source and inorganic molecules as an energy source.

• Discovered in 1977 nutrients discharged through

oceanic rift. Chemosynthetic bacteria

are the autotrophs that the communities depend on.

Free-living forms. Living within tissue of

invertebrates.

http://www.youtube.com/watch?v=AlHJqA8YkoI

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Heterotrophs• Need to eat other things – source of carbon

and energy• Three Feeding Methods of Heterotrophs:

Herbivores: Feed on plants. Carnivores: Feed on animal flesh. Detritivores: Feed on non-living organic

matter. Match ‘em!

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Chemical Composition and Nutrient Requirements

• Five elements make up 93-97% of biomass of plants, animals, fungi and bacteria: Carbon Oxygen Hydrogen Nitrogen Phosphorus

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It be dangerous to eat sometimes!!!Herbivores

• Must overcome plant physical and chemical defenses. Physical

Cellulose; lignin; silica Chemical

Toxins Digestion Reducing Compounds

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Prey Defenses: Aposematic

Coloring - Warning colors.

Mullerian mimicry: Comimicry among several species of noxious organisms.

Batesian mimicry: Harmless species mimic noxious species.

It be dangerous to eat sometimes!!!Carnivores

http://www.youtube.com/watch?v=lXi1fQ50Bc8

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Predators & Prey• Predators are usually selection agents for prey

Usually eliminate more conspicuous members of a population (less adaptive).

• Predator and prey species are engaged in a co-evolutionary race.

http://www.youtube.com/watch?v=LyRA807djLc

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How do organisms choose to eat? Optimal Foraging Theory – Feeding is an optimizing

process!• Natural selection favors individuals within a

population that are more effective at acquiring energy

• More abundant/larger prey yields larger energy return.

Must consider costs!

http://www.youtube.com/watch?v=d7avgP0IdPQ

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Optimal Foraging By Plants???

• Is this possible??? How so???

Plants in environments with abundant nutrients but little light will spend less energy on root growth

Plants in environments with abundant light but poor nutrients will spend less energy on stem and leaf growth